Conventional methods for drycleaning use a chlorinated hydrocarbon solvent, most commonly perchloroethylene (PERC) in combination with small amounts of water and detergents. While PERC is fabric-safe, non-flammable, and easily recycled, it has come under attack in recent years as an environmental and health hazard. In particular, PERC is listed as a Hazardous Air Pollutant (HAP), it is non-biodegradable, and it is a probable human carcinogen.
In recent years, the industry has responded with less-toxic alternatives to PERC, including hydrocarbons (e.g., EcoSolv™ drycleaning fluid from CPChem) and glycol ethers. One glycol ether, dipropylene glycol n-propyl ether (DPnP), has been used in combination with other essential components. For example, DPnP has been used with a polysulfonic acid, a substrate, and other components (see, e.g., U.S. Pat. Nos. 6,086,634 and 6,036,727) for at-home drycleaning in a conventional clothes dryer. The polysulfonic acid is a critical component that aids in cleaning and freshening the soiled fabric.
Another environmentally friendly alternative to PERC, available from GreenEarth Cleaning, uses a cyclic siloxane, optionally in combination with a glycol ether (which may be DPnP) or another organic solvent (see, e.g., U.S. Pat. Nos. 6,042,617 and 6,063,135). The cyclic siloxane has a desirable flash point, fabric-safe qualities, and good solvency for oily soils. While they do have low toxicity, siloxanes have relatively low cleaning power and are preferably avoided.
Other glycol ethers have been recommended for use in drycleaning, most notably propylene glycol tert-butyl ether (PTB), propylene glycol n-butyl ether (PNB), dipropylene glycol tert-butyl ether (DPTB) and dipropylene glycol n-butyl ether (DPNB). See, for example, U.S. Pat. Nos. 5,888,250, 6,156,074, 6,273,919, and 6,350,287, all assigned to Rynex Holdings, Ltd. In particular, the '919 and '287 patents teach DPTB as an alternative with significant advantages over PERC. DPTB has a high flash point and good detergency. The compositions taught for use are DPTB/water (>9:1 by weight) mixtures. The use of glycol ethers, including DPTB, represents a significant step toward replacing PERC in drycleaning.
Good progress has been made to date, but the industry continues to need a better replacement for PERC. In particular, the industry would benefit from ways to dryclean fabrics and fibers with fluids that are also free of siloxanes, polysulfonic acids, or other complex or expensive components. An improved drycleaning method would be effective for both oily soils (e.g., butter or animal fat) and more water-soluble soils (e.g., tea or blood). Always of interest, especially to parents of young children, is a cleaning method that is more effective for removing grass stains. Preferably, the cleaning method would help to prevent redeposition of soils (a problem for PERC if PERC is used without detergents). An ideal cleaner would use readily available, inexpensive components, and would outperform commercially available alternatives to PERC such as those based on hydrocarbons or DPTB. Finally, the cleaning method must not harm the fabric. In particular, the method must not cause undue shrinkage (i.e., more than about 2%).